login: reduce file-descriptors cleanup overhead

[thirdparty/util-linux.git] / login-utils / login.c

/*
 * login(1)
 *
 * This program is derived from 4.3 BSD software and is subject to the
 * copyright notice below.
 *
 * Copyright (C) 2011 Karel Zak <kzak@redhat.com>
 * Rewritten to PAM-only version.
 *
 * Michael Glad (glad@daimi.dk)
 * Computer Science Department, Aarhus University, Denmark
 * 1990-07-04
 *
 * Copyright (c) 1980, 1987, 1988 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#include <sys/param.h>
#include <stdio.h>
#include <ctype.h>
#include <unistd.h>
#include <getopt.h>
#include <memory.h>
#include <time.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/file.h>
#include <termios.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/wait.h>
#include <signal.h>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <utmpx.h>
#ifdef HAVE_LASTLOG_H
# include <lastlog.h>
#endif
#include <stdlib.h>
#include <sys/syslog.h>
#ifdef HAVE_LINUX_MAJOR_H
# include <linux/major.h>
#endif
#include <netdb.h>
#include <security/pam_appl.h>
#ifdef HAVE_SECURITY_PAM_MISC_H
# include <security/pam_misc.h>
#elif defined(HAVE_SECURITY_OPENPAM_H)
# include <security/openpam.h>
#endif
#include <sys/sendfile.h>

#ifdef HAVE_LIBAUDIT
# include <libaudit.h>
#endif

#include "c.h"
#include "setproctitle.h"
#include "pathnames.h"
#include "strutils.h"
#include "nls.h"
#include "env.h"
#include "xalloc.h"
#include "all-io.h"
#include "fileutils.h"
#include "ttyutils.h"
#include "pwdutils.h"

#include "logindefs.h"

#define is_pam_failure(_rc)     ((_rc) != PAM_SUCCESS)

#define LOGIN_MAX_TRIES        3
#define LOGIN_EXIT_TIMEOUT     5
#define LOGIN_TIMEOUT          60

#ifdef USE_TTY_GROUP
# define TTY_MODE 0620
#else
# define TTY_MODE 0600
#endif

#define TTYGRPNAME      "tty"   /* name of group to own ttys */
#define VCS_PATH_MAX    64

/*
 * Login control struct
 */
struct login_context {
        const char      *tty_path;      /* ttyname() return value */
        const char      *tty_name;      /* tty_path without /dev prefix */
        const char      *tty_number;    /* end of the tty_path */
        mode_t          tty_mode;       /* chmod() mode */

        const char      *username;      /* points to PAM, pwd or cmd_username */
        char            *cmd_username;  /* username specified on command line */


        struct passwd   *pwd;           /* user info */
        char            *pwdbuf;        /* pwd strings */

        pam_handle_t    *pamh;          /* PAM handler */
        struct pam_conv conv;           /* PAM conversation */

#ifdef LOGIN_CHOWN_VCS
        char            vcsn[VCS_PATH_MAX];     /* virtual console name */
        char            vcsan[VCS_PATH_MAX];
#endif

        char            *thishost;              /* this machine */
        char            *thisdomain;            /* this machine's domain */
        char            *hostname;              /* remote machine */
        char            hostaddress[16];        /* remote address */

        pid_t           pid;
        int             quiet;          /* 1 if hush file exists */

        unsigned int    remote:1,       /* login -h */
                        nohost:1,       /* login -H */
                        noauth:1,       /* login -f */
                        keep_env:1;     /* login -p */
};

/*
 * This bounds the time given to login.  Not a define, so it can
 * be patched on machines where it's too small.
 */
static unsigned int timeout = LOGIN_TIMEOUT;
static int child_pid = 0;
static volatile int got_sig = 0;
static char timeout_msg[128];

#ifdef LOGIN_CHOWN_VCS
/* true if the filedescriptor fd is a console tty, very Linux specific */
static int is_consoletty(int fd)
{
        struct stat stb;

        if ((fstat(fd, &stb) >= 0)
            && (major(stb.st_rdev) == TTY_MAJOR)
            && (minor(stb.st_rdev) < 64)) {
                return 1;
        }
        return 0;
}
#endif


/*
 * Robert Ambrose writes:
 * A couple of my users have a problem with login processes hanging around
 * soaking up pts's.  What they seem to hung up on is trying to write out the
 * message 'Login timed out after %d seconds' when the connection has already
 * been dropped.
 * What I did was add a second timeout while trying to write the message, so
 * the process just exits if the second timeout expires.
 */
static void __attribute__ ((__noreturn__))
timedout2(int sig __attribute__ ((__unused__)))
{
        struct termios ti;

        /* reset echo */
        tcgetattr(0, &ti);
        ti.c_lflag |= ECHO;
        tcsetattr(0, TCSANOW, &ti);
        _exit(EXIT_SUCCESS);    /* %% */
}

static void timedout(int sig __attribute__ ((__unused__)))
{
        signal(SIGALRM, timedout2);
        alarm(10);
        ignore_result( write(STDERR_FILENO, timeout_msg, strlen(timeout_msg)) );
        signal(SIGALRM, SIG_IGN);
        alarm(0);
        timedout2(0);
}

/*
 * This handler allows to inform a shell about signals to login. If you have
 * (root) permissions, you can kill all login children by one signal to the
 * login process.
 *
 * Also, a parent who is session leader is able (before setsid() in the child)
 * to inform the child when the controlling tty goes away (e.g. modem hangup).
 */
static void sig_handler(int signal)
{
        if (child_pid)
                kill(-child_pid, signal);
        else
                got_sig = 1;
        if (signal == SIGTERM)
                kill(-child_pid, SIGHUP);       /* because the shell often ignores SIGTERM */
}

/*
 * Let us delay all exit() calls when the user is not authenticated
 * or the session not fully initialized (loginpam_session()).
 */
static void __attribute__ ((__noreturn__)) sleepexit(int eval)
{
        sleep((unsigned int)getlogindefs_num("FAIL_DELAY", LOGIN_EXIT_TIMEOUT));
        exit(eval);
}

static const char *get_thishost(struct login_context *cxt, const char **domain)
{
        if (!cxt->thishost) {
                cxt->thishost = xgethostname();
                if (!cxt->thishost) {
                        if (domain)
                                *domain = NULL;
                        return NULL;
                }
                cxt->thisdomain = strchr(cxt->thishost, '.');
                if (cxt->thisdomain)
                        *cxt->thisdomain++ = '\0';
        }

        if (domain)
                *domain = cxt->thisdomain;
        return cxt->thishost;
}

/*
 * Output the /etc/motd file.
 *
 * It determines the name of a login announcement file and outputs it to the
 * user's terminal at login time.  The MOTD_FILE configuration option is a
 * colon-delimited list of filenames.  An empty MOTD_FILE option disables
 * message-of-the-day printing completely.
 */
static void motd(void)
{
        char *motdlist, *motdfile;
        const char *mb;

        mb = getlogindefs_str("MOTD_FILE", _PATH_MOTDFILE);
        if (!mb || !*mb)
                return;

        motdlist = xstrdup(mb);

        for (motdfile = strtok(motdlist, ":"); motdfile;
             motdfile = strtok(NULL, ":")) {

                struct stat st;
                int fd;

                fd = open(motdfile, O_RDONLY, 0);
                if (fd < 0)
                        continue;
                if (!fstat(fd, &st) && st.st_size)
                        sendfile(fileno(stdout), fd, NULL, st.st_size);
                close(fd);
        }

        free(motdlist);
}

/*
 * Nice and simple code provided by Linus Torvalds 16-Feb-93.
 * Non-blocking stuff by Maciej W. Rozycki, macro@ds2.pg.gda.pl, 1999.
 *
 * He writes: "Login performs open() on a tty in a blocking mode.
 * In some cases it may make login wait in open() for carrier infinitely,
 * for example if the line is a simplistic case of a three-wire serial
 * connection. I believe login should open the line in non-blocking mode,
 * leaving the decision to make a connection to getty (where it actually
 * belongs)."
 */
static void open_tty(const char *tty)
{
        int i, fd, flags;

        fd = open(tty, O_RDWR | O_NONBLOCK);
        if (fd == -1) {
                syslog(LOG_ERR, _("FATAL: can't reopen tty: %m"));
                sleepexit(EXIT_FAILURE);
        }

        if (!isatty(fd)) {
                close(fd);
                syslog(LOG_ERR, _("FATAL: %s is not a terminal"), tty);
                sleepexit(EXIT_FAILURE);
        }

        flags = fcntl(fd, F_GETFL);
        flags &= ~O_NONBLOCK;
        fcntl(fd, F_SETFL, flags);

        for (i = 0; i < fd; i++)
                close(i);
        for (i = 0; i < 3; i++)
                if (fd != i)
                        dup2(fd, i);
        if (fd >= 3)
                close(fd);
}

#define chown_err(_what, _uid, _gid) \
                syslog(LOG_ERR, _("chown (%s, %lu, %lu) failed: %m"), \
                        (_what), (unsigned long) (_uid), (unsigned long) (_gid))

#define chmod_err(_what, _mode) \
                syslog(LOG_ERR, _("chmod (%s, %u) failed: %m"), (_what), (_mode))

static void chown_tty(struct login_context *cxt)
{
        const char *grname;
        uid_t uid = cxt->pwd->pw_uid;
        gid_t gid = cxt->pwd->pw_gid;

        grname = getlogindefs_str("TTYGROUP", TTYGRPNAME);
        if (grname && *grname) {
                struct group *gr = getgrnam(grname);
                if (gr) /* group by name */
                        gid = gr->gr_gid;
                else    /* group by ID */
                        gid = (gid_t) getlogindefs_num("TTYGROUP", gid);
        }
        if (fchown(0, uid, gid))                                /* tty */
                chown_err(cxt->tty_name, uid, gid);
        if (fchmod(0, cxt->tty_mode))
                chmod_err(cxt->tty_name, cxt->tty_mode);

#ifdef LOGIN_CHOWN_VCS
        if (is_consoletty(0)) {
                if (chown(cxt->vcsn, uid, gid))                 /* vcs */
                        chown_err(cxt->vcsn, uid, gid);
                if (chmod(cxt->vcsn, cxt->tty_mode))
                        chmod_err(cxt->vcsn, cxt->tty_mode);

                if (chown(cxt->vcsan, uid, gid))                /* vcsa */
                        chown_err(cxt->vcsan, uid, gid);
                if (chmod(cxt->vcsan, cxt->tty_mode))
                        chmod_err(cxt->vcsan, cxt->tty_mode);
        }
#endif
}

/*
 * Reads the current terminal path and initializes cxt->tty_* variables.
 */
static void init_tty(struct login_context *cxt)
{
        struct stat st;
        struct termios tt, ttt;

        cxt->tty_mode = (mode_t) getlogindefs_num("TTYPERM", TTY_MODE);

        get_terminal_name(&cxt->tty_path, &cxt->tty_name, &cxt->tty_number);

        /*
         * In case login is suid it was possible to use a hardlink as stdin
         * and exploit races for a local root exploit. (Wojciech Purczynski).
         *
         * More precisely, the problem is  ttyn := ttyname(0); ...; chown(ttyn);
         * here ttyname() might return "/tmp/x", a hardlink to a pseudotty.
         * All of this is a problem only when login is suid, which it isn't.
         */
        if (!cxt->tty_path || !*cxt->tty_path ||
            lstat(cxt->tty_path, &st) != 0 || !S_ISCHR(st.st_mode) ||
            (st.st_nlink > 1 && strncmp(cxt->tty_path, "/dev/", 5)) ||
            access(cxt->tty_path, R_OK | W_OK) != 0) {

                syslog(LOG_ERR, _("FATAL: bad tty"));
                sleepexit(EXIT_FAILURE);
        }

#ifdef LOGIN_CHOWN_VCS
        if (cxt->tty_number) {
                /* find names of Virtual Console devices, for later mode change */
                snprintf(cxt->vcsn, sizeof(cxt->vcsn), "/dev/vcs%s", cxt->tty_number);
                snprintf(cxt->vcsan, sizeof(cxt->vcsan), "/dev/vcsa%s", cxt->tty_number);
        }
#endif

        tcgetattr(0, &tt);
        ttt = tt;
        ttt.c_cflag &= ~HUPCL;

        if ((fchown(0, 0, 0) || fchmod(0, cxt->tty_mode)) && errno != EROFS) {

                syslog(LOG_ERR, _("FATAL: %s: change permissions failed: %m"),
                                cxt->tty_path);
                sleepexit(EXIT_FAILURE);
        }

        /* Kill processes left on this tty */
        tcsetattr(0, TCSANOW, &ttt);

        /*
         * Let's close file descriptors before vhangup
         * https://lkml.org/lkml/2012/6/5/145
         */
        close(STDIN_FILENO);
        close(STDOUT_FILENO);
        close(STDERR_FILENO);

        signal(SIGHUP, SIG_IGN);        /* so vhangup() won't kill us */
        vhangup();
        signal(SIGHUP, SIG_DFL);

        /* open stdin,stdout,stderr to the tty */
        open_tty(cxt->tty_path);

        /* restore tty modes */
        tcsetattr(0, TCSAFLUSH, &tt);
}


/*
 * Logs failed login attempts in _PATH_BTMP, if it exists.
 * Must be called only with username the name of an actual user.
 * The most common login failure is to give password instead of username.
 */
static void log_btmp(struct login_context *cxt)
{
        struct utmpx ut;
        struct timeval tv;

        memset(&ut, 0, sizeof(ut));

        str2memcpy(ut.ut_user,
                cxt->username ? cxt->username : "(unknown)",
                sizeof(ut.ut_user));

        if (cxt->tty_number)
                str2memcpy(ut.ut_id, cxt->tty_number, sizeof(ut.ut_id));
        if (cxt->tty_name)
                str2memcpy(ut.ut_line, cxt->tty_name, sizeof(ut.ut_line));

        gettimeofday(&tv, NULL);
        ut.ut_tv.tv_sec = tv.tv_sec;
        ut.ut_tv.tv_usec = tv.tv_usec;

        ut.ut_type = LOGIN_PROCESS;     /* XXX doesn't matter */
        ut.ut_pid = cxt->pid;

        if (cxt->hostname) {
                str2memcpy(ut.ut_host, cxt->hostname, sizeof(ut.ut_host));
                if (*cxt->hostaddress)
                        memcpy(&ut.ut_addr_v6, cxt->hostaddress,
                               sizeof(ut.ut_addr_v6));
        }

        updwtmpx(_PATH_BTMP, &ut);
}


#ifdef HAVE_LIBAUDIT
static void log_audit(struct login_context *cxt, int status)
{
        int audit_fd;
        struct passwd *pwd = cxt->pwd;

        audit_fd = audit_open();
        if (audit_fd == -1)
                return;
        if (!pwd && cxt->username)
                pwd = getpwnam(cxt->username);

        audit_log_acct_message(audit_fd,
                               AUDIT_USER_LOGIN,
                               NULL,
                               "login",
                               cxt->username ? cxt->username : "(unknown)",
                               pwd ? pwd->pw_uid : (unsigned int) -1,
                               cxt->hostname,
                               NULL,
                               cxt->tty_name,
                               status);

        close(audit_fd);
}
#else                           /* !HAVE_LIBAUDIT */
# define log_audit(cxt, status)
#endif                          /* HAVE_LIBAUDIT */

static void log_lastlog(struct login_context *cxt)
{
        struct sigaction sa, oldsa_xfsz;
        struct lastlog ll;
        time_t t;
        int fd;

        if (!cxt->pwd)
                return;

        if (cxt->pwd->pw_uid > (uid_t) getlogindefs_num("LASTLOG_UID_MAX", ULONG_MAX))
                return;

        /* lastlog is huge on systems with large UIDs, ignore SIGXFSZ */
        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = SIG_IGN;
        sigaction(SIGXFSZ, &sa, &oldsa_xfsz);

        fd = open(_PATH_LASTLOG, O_RDWR, 0);
        if (fd < 0)
                goto done;

        if (lseek(fd, (off_t) cxt->pwd->pw_uid * sizeof(ll), SEEK_SET) == -1)
                goto done;

        /*
         * Print last log message.
         */
        if (!cxt->quiet) {
                if (read(fd, (char *)&ll, sizeof(ll)) == sizeof(ll) &&
                                                        ll.ll_time != 0) {
                        time_t ll_time = (time_t) ll.ll_time;

                        printf(_("Last login: %.*s "), 24 - 5, ctime(&ll_time));
                        if (*ll.ll_host != '\0')
                                printf(_("from %.*s\n"),
                                       (int)sizeof(ll.ll_host), ll.ll_host);
                        else
                                printf(_("on %.*s\n"),
                                       (int)sizeof(ll.ll_line), ll.ll_line);
                }
                if (lseek(fd, (off_t) cxt->pwd->pw_uid * sizeof(ll), SEEK_SET) == -1)
                        goto done;
        }

        memset((char *)&ll, 0, sizeof(ll));

        time(&t);
        ll.ll_time = t;         /* ll_time is always 32bit */

        if (cxt->tty_name)
                str2memcpy(ll.ll_line, cxt->tty_name, sizeof(ll.ll_line));
        if (cxt->hostname)
                str2memcpy(ll.ll_host, cxt->hostname, sizeof(ll.ll_host));

        if (write_all(fd, (char *)&ll, sizeof(ll)))
                warn(_("write lastlog failed"));
done:
        if (fd >= 0)
                close(fd);

        sigaction(SIGXFSZ, &oldsa_xfsz, NULL);          /* restore original setting */
}

/*
 * Update wtmp and utmp logs.
 */
static void log_utmp(struct login_context *cxt)
{
        struct utmpx ut;
        struct utmpx *utp;
        struct timeval tv;

        utmpxname(_PATH_UTMP);
        setutxent();

        /* Find pid in utmp.
         *
         * login sometimes overwrites the runlevel entry in /var/run/utmp,
         * confusing sysvinit. I added a test for the entry type, and the
         * problem was gone. (In a runlevel entry, st_pid is not really a pid
         * but some number calculated from the previous and current runlevel.)
         * -- Michael Riepe <michael@stud.uni-hannover.de>
         */
        while ((utp = getutxent()))
                if (utp->ut_pid == cxt->pid
                    && utp->ut_type >= INIT_PROCESS
                    && utp->ut_type <= DEAD_PROCESS)
                        break;

        /* If we can't find a pre-existing entry by pid, try by line.
         * BSD network daemons may rely on this. */
        if (utp == NULL && cxt->tty_name) {
                setutxent();
                ut.ut_type = LOGIN_PROCESS;
                str2memcpy(ut.ut_line, cxt->tty_name, sizeof(ut.ut_line));
                utp = getutxline(&ut);
        }

        /* If we can't find a pre-existing entry by pid and line, try it by id.
         * Very stupid telnetd daemons don't set up utmp at all. (kzak) */
        if (utp == NULL && cxt->tty_number) {
             setutxent();
             ut.ut_type = DEAD_PROCESS;
             str2memcpy(ut.ut_id, cxt->tty_number, sizeof(ut.ut_id));
             utp = getutxid(&ut);
        }

        if (utp)
                memcpy(&ut, utp, sizeof(ut));
        else
                /* some gettys/telnetds don't initialize utmp... */
                memset(&ut, 0, sizeof(ut));

        if (cxt->tty_number && ut.ut_id[0] == 0)
                str2memcpy(ut.ut_id, cxt->tty_number, sizeof(ut.ut_id));
        if (cxt->username)
                str2memcpy(ut.ut_user, cxt->username, sizeof(ut.ut_user));
        if (cxt->tty_name)
                str2memcpy(ut.ut_line, cxt->tty_name, sizeof(ut.ut_line));

        gettimeofday(&tv, NULL);
        ut.ut_tv.tv_sec = tv.tv_sec;
        ut.ut_tv.tv_usec = tv.tv_usec;
        ut.ut_type = USER_PROCESS;
        ut.ut_pid = cxt->pid;
        if (cxt->hostname) {
                str2memcpy(ut.ut_host, cxt->hostname, sizeof(ut.ut_host));
                if (*cxt->hostaddress)
                        memcpy(&ut.ut_addr_v6, cxt->hostaddress,
                               sizeof(ut.ut_addr_v6));
        }

        pututxline(&ut);
        endutxent();

        updwtmpx(_PATH_WTMP, &ut);
}

static void log_syslog(struct login_context *cxt)
{
        struct passwd *pwd = cxt->pwd;

        if (!cxt->tty_name)
                return;

        if (!strncmp(cxt->tty_name, "ttyS", 4))
                syslog(LOG_INFO, _("DIALUP AT %s BY %s"),
                       cxt->tty_name, pwd->pw_name);

        if (!pwd->pw_uid) {
                if (cxt->hostname)
                        syslog(LOG_NOTICE, _("ROOT LOGIN ON %s FROM %s"),
                               cxt->tty_name, cxt->hostname);
                else
                        syslog(LOG_NOTICE, _("ROOT LOGIN ON %s"), cxt->tty_name);
        } else {
                if (cxt->hostname)
                        syslog(LOG_INFO, _("LOGIN ON %s BY %s FROM %s"),
                               cxt->tty_name, pwd->pw_name, cxt->hostname);
                else
                        syslog(LOG_INFO, _("LOGIN ON %s BY %s"), cxt->tty_name,
                               pwd->pw_name);
        }
}

/* encapsulate stupid "void **" pam_get_item() API */
static int loginpam_get_username(pam_handle_t *pamh, const char **name)
{
        const void *item = (const void *)*name;
        int rc;
        rc = pam_get_item(pamh, PAM_USER, &item);
        *name = (const char *)item;
        return rc;
}

static void loginpam_err(pam_handle_t *pamh, int retcode)
{
        const char *msg = pam_strerror(pamh, retcode);

        if (msg) {
                fprintf(stderr, "\n%s\n", msg);
                syslog(LOG_ERR, "%s", msg);
        }
        pam_end(pamh, retcode);
        sleepexit(EXIT_FAILURE);
}

/*
 * Composes "<host> login: " string; or returns "login: " if -H is given or
 * LOGIN_PLAIN_PROMPT=yes configured.
 */
static const char *loginpam_get_prompt(struct login_context *cxt)
{
        const char *host;
        char *prompt, *dflt_prompt = _("login: ");
        size_t sz;

        if (cxt->nohost)
                return dflt_prompt;     /* -H on command line */

        if (getlogindefs_bool("LOGIN_PLAIN_PROMPT", 0) == 1)
                return dflt_prompt;

        if (!(host = get_thishost(cxt, NULL)))
                return dflt_prompt;

        sz = strlen(host) + 1 + strlen(dflt_prompt) + 1;
        prompt = xmalloc(sz);
        snprintf(prompt, sz, "%s %s", host, dflt_prompt);

        return prompt;
}

static pam_handle_t *init_loginpam(struct login_context *cxt)
{
        pam_handle_t *pamh = NULL;
        int rc;

        /*
         * username is initialized to NULL and if specified on the command line
         * it is set.  Therefore, we are safe not setting it to anything.
         */
        rc = pam_start(cxt->remote ? "remote" : "login",
                       cxt->username, &cxt->conv, &pamh);
        if (rc != PAM_SUCCESS) {
                warnx(_("PAM failure, aborting: %s"), pam_strerror(pamh, rc));
                syslog(LOG_ERR, _("Couldn't initialize PAM: %s"),
                       pam_strerror(pamh, rc));
                sleepexit(EXIT_FAILURE);
        }

        /* hostname & tty are either set to NULL or their correct values,
         * depending on how much we know. */
        rc = pam_set_item(pamh, PAM_RHOST, cxt->hostname);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        rc = pam_set_item(pamh, PAM_TTY, cxt->tty_name);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        /*
         * Andrew.Taylor@cal.montage.ca: Provide a user prompt to PAM so that
         * the "login: " prompt gets localized. Unfortunately, PAM doesn't have
         * an interface to specify the "Password: " string (yet).
         */
        rc = pam_set_item(pamh, PAM_USER_PROMPT, loginpam_get_prompt(cxt));
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        /* We don't need the original username. We have to follow PAM. */
        cxt->username = NULL;
        cxt->pamh = pamh;

        return pamh;
}

static void loginpam_auth(struct login_context *cxt)
{
        int rc, show_unknown;
        unsigned int retries, failcount = 0;
        const char *hostname = cxt->hostname ? cxt->hostname :
                               cxt->tty_name ? cxt->tty_name : "<unknown>";
        pam_handle_t *pamh = cxt->pamh;

        /* if we didn't get a user on the command line, set it to NULL */
        loginpam_get_username(pamh, &cxt->username);

        show_unknown = getlogindefs_bool("LOG_UNKFAIL_ENAB", 0);
        retries = getlogindefs_num("LOGIN_RETRIES", LOGIN_MAX_TRIES);

        /*
         * There may be better ways to deal with some of these conditions, but
         * at least this way I don't think we'll be giving away information...
         *
         * Perhaps someday we can trust that all PAM modules will pay attention
         * to failure count and get rid of LOGIN_MAX_TRIES?
         */
        rc = pam_authenticate(pamh, 0);

        while ((++failcount < retries) &&
               ((rc == PAM_AUTH_ERR) ||
                (rc == PAM_USER_UNKNOWN) ||
                (rc == PAM_CRED_INSUFFICIENT) ||
                (rc == PAM_AUTHINFO_UNAVAIL))) {

                if (rc == PAM_USER_UNKNOWN && !show_unknown)
                        /*
                         * Logging unknown usernames may be a security issue if
                         * a user enters her password instead of her login name.
                         */
                        cxt->username = NULL;
                else
                        loginpam_get_username(pamh, &cxt->username);

                syslog(LOG_NOTICE,
                       _("FAILED LOGIN %u FROM %s FOR %s, %s"),
                       failcount, hostname,
                       cxt->username ? cxt->username : "(unknown)",
                       pam_strerror(pamh, rc));

                log_btmp(cxt);
                log_audit(cxt, 0);

                fprintf(stderr, _("Login incorrect\n\n"));

                pam_set_item(pamh, PAM_USER, NULL);
                rc = pam_authenticate(pamh, 0);
        }

        if (is_pam_failure(rc)) {

                if (rc == PAM_USER_UNKNOWN && !show_unknown)
                        cxt->username = NULL;
                else
                        loginpam_get_username(pamh, &cxt->username);

                if (rc == PAM_MAXTRIES)
                        syslog(LOG_NOTICE,
                               _("TOO MANY LOGIN TRIES (%u) FROM %s FOR %s, %s"),
                               failcount, hostname,
                               cxt->username ? cxt->username : "(unknown)",
                               pam_strerror(pamh, rc));
                else
                        syslog(LOG_NOTICE,
                               _("FAILED LOGIN SESSION FROM %s FOR %s, %s"),
                               hostname,
                               cxt->username ? cxt->username : "(unknown)",
                               pam_strerror(pamh, rc));

                log_btmp(cxt);
                log_audit(cxt, 0);

                fprintf(stderr, _("\nLogin incorrect\n"));
                pam_end(pamh, rc);
                sleepexit(EXIT_SUCCESS);
        }
}

static void loginpam_acct(struct login_context *cxt)
{
        int rc;
        pam_handle_t *pamh = cxt->pamh;

        rc = pam_acct_mgmt(pamh, 0);

        if (rc == PAM_NEW_AUTHTOK_REQD)
                rc = pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK);

        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        /*
         * Grab the user information out of the password file for future use.
         * First get the username that we are actually using, though.
         */
        rc = loginpam_get_username(pamh, &cxt->username);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        if (!cxt->username || !*cxt->username) {
                warnx(_("\nSession setup problem, abort."));
                syslog(LOG_ERR, _("NULL user name. Abort."));
                pam_end(pamh, PAM_SYSTEM_ERR);
                sleepexit(EXIT_FAILURE);
        }
}

/*
 * Note that the position of the pam_setcred() call is discussable:
 *
 *  - the PAM docs recommend pam_setcred() before pam_open_session()
 *  - but the original RFC http://www.opengroup.org/rfc/mirror-rfc/rfc86.0.txt
 *    uses pam_setcred() after pam_open_session()
 *
 * The old login versions (before year 2011) followed the RFC. This is probably
 * not optimal, because there could be a dependence between some session modules
 * and the user's credentials.
 *
 * The best is probably to follow openssh and call pam_setcred() before and
 * after pam_open_session().                -- kzak@redhat.com (18-Nov-2011)
 *
 */
static void loginpam_session(struct login_context *cxt)
{
        int rc;
        pam_handle_t *pamh = cxt->pamh;

        rc = pam_setcred(pamh, PAM_ESTABLISH_CRED);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        rc = pam_open_session(pamh, 0);
        if (is_pam_failure(rc)) {
                pam_setcred(cxt->pamh, PAM_DELETE_CRED);
                loginpam_err(pamh, rc);
        }

        rc = pam_setcred(pamh, PAM_REINITIALIZE_CRED);
        if (is_pam_failure(rc)) {
                pam_close_session(pamh, 0);
                loginpam_err(pamh, rc);
        }
}

/*
 * Detach the controlling terminal, fork, restore syslog stuff, and create
 * a new session.
 */
static void fork_session(struct login_context *cxt)
{
        struct sigaction sa, oldsa_hup, oldsa_term;

        signal(SIGALRM, SIG_DFL);
        signal(SIGQUIT, SIG_DFL);
        signal(SIGTSTP, SIG_IGN);

        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = SIG_IGN;
        sigaction(SIGINT, &sa, NULL);

        sigaction(SIGHUP, &sa, &oldsa_hup);     /* ignore when TIOCNOTTY */

        /*
         * Detach the controlling tty.
         * We don't need the tty in a parent who only waits for a child.
         * The child calls setsid() that detaches from the tty as well.
         */
        ioctl(0, TIOCNOTTY, NULL);

        /*
         * We have to beware of SIGTERM, because leaving a PAM session
         * without pam_close_session() is a pretty bad thing.
         */
        sa.sa_handler = sig_handler;
        sigaction(SIGHUP, &sa, NULL);
        sigaction(SIGTERM, &sa, &oldsa_term);

        closelog();

        /*
         * We must fork before setuid(), because we need to call
         * pam_close_session() as root.
         */
        child_pid = fork();
        if (child_pid < 0) {
                warn(_("fork failed"));

                pam_setcred(cxt->pamh, PAM_DELETE_CRED);
                pam_end(cxt->pamh, pam_close_session(cxt->pamh, 0));
                sleepexit(EXIT_FAILURE);
        }

        if (child_pid) {
                /*
                 * parent - wait for child to finish, then clean up session
                 */
                close(0);
                close(1);
                close(2);
                free_getlogindefs_data();

                sa.sa_handler = SIG_IGN;
                sigaction(SIGQUIT, &sa, NULL);
                sigaction(SIGINT, &sa, NULL);

                /* wait as long as any child is there */
                while (wait(NULL) == -1 && errno == EINTR) ;
                openlog("login", LOG_ODELAY, LOG_AUTHPRIV);

                pam_setcred(cxt->pamh, PAM_DELETE_CRED);
                pam_end(cxt->pamh, pam_close_session(cxt->pamh, 0));
                exit(EXIT_SUCCESS);
        }

        /*
         * child
         */
        sigaction(SIGHUP, &oldsa_hup, NULL);            /* restore old state */
        sigaction(SIGTERM, &oldsa_term, NULL);
        if (got_sig)
                exit(EXIT_FAILURE);

        /*
         * Problem: if the user's shell is a shell like ash that doesn't do
         * setsid() or setpgrp(), then a ctrl-\, sending SIGQUIT to every
         * process in the pgrp, will kill us.
         */

        /* start new session */
        setsid();

        /* make sure we have a controlling tty */
        open_tty(cxt->tty_path);
        openlog("login", LOG_ODELAY, LOG_AUTHPRIV);     /* reopen */

        /*
         * TIOCSCTTY: steal tty from other process group.
         */
        if (ioctl(0, TIOCSCTTY, 1))
                syslog(LOG_ERR, _("TIOCSCTTY failed: %m"));
        signal(SIGINT, SIG_DFL);
}

/*
 * Initialize $TERM, $HOME, ...
 */
static void init_environ(struct login_context *cxt)
{
        struct passwd *pwd = cxt->pwd;
        char *termenv, **env;
        char tmp[PATH_MAX];
        int len, i;

        termenv = getenv("TERM");
        if (termenv)
                termenv = xstrdup(termenv);

        /* destroy environment unless user has requested preservation (-p) */
        if (!cxt->keep_env) {
                environ = xmalloc(sizeof(char *));
                memset(environ, 0, sizeof(char *));
        }

        xsetenv("HOME", pwd->pw_dir, 0);        /* legal to override */
        xsetenv("USER", pwd->pw_name, 1);
        xsetenv("SHELL", pwd->pw_shell, 1);
        xsetenv("TERM", termenv ? termenv : "dumb", 1);
        free(termenv);

        if (pwd->pw_uid) {
                if (logindefs_setenv("PATH", "ENV_PATH", _PATH_DEFPATH) != 0)
                        err(EXIT_FAILURE, _("failed to set the %s environment variable"), "PATH");

        } else if (logindefs_setenv("PATH", "ENV_ROOTPATH", NULL) != 0 &&
                   logindefs_setenv("PATH", "ENV_SUPATH", _PATH_DEFPATH_ROOT) != 0) {
                        err(EXIT_FAILURE, _("failed to set the %s environment variable"), "PATH");
        }

        /* mailx will give a funny error msg if you forget this one */
        len = snprintf(tmp, sizeof(tmp), "%s/%s", _PATH_MAILDIR, pwd->pw_name);
        if (len > 0 && (size_t) len < sizeof(tmp))
                xsetenv("MAIL", tmp, 0);

        /* LOGNAME is not documented in login(1) but HP-UX 6.5 does it. We'll
         * not allow modifying it.
         */
        xsetenv("LOGNAME", pwd->pw_name, 1);

        env = pam_getenvlist(cxt->pamh);
        for (i = 0; env && env[i]; i++)
                putenv(env[i]);
}

/*
 * This is called for the -h option, initializes cxt->{hostname,hostaddress}.
 */
static void init_remote_info(struct login_context *cxt, char *remotehost)
{
        const char *domain;
        char *p;
        struct addrinfo hints, *info = NULL;

        cxt->remote = 1;

        get_thishost(cxt, &domain);

        if (domain && (p = strchr(remotehost, '.')) &&
            strcasecmp(p + 1, domain) == 0)
                *p = '\0';

        cxt->hostname = xstrdup(remotehost);

        memset(&hints, 0, sizeof(hints));
        hints.ai_flags = AI_ADDRCONFIG;
        cxt->hostaddress[0] = 0;

        if (getaddrinfo(cxt->hostname, NULL, &hints, &info) == 0 && info) {
                if (info->ai_family == AF_INET) {
                        struct sockaddr_in *sa =
                                    (struct sockaddr_in *) info->ai_addr;

                        memcpy(cxt->hostaddress, &(sa->sin_addr), sizeof(sa->sin_addr));

                } else if (info->ai_family == AF_INET6) {
                        struct sockaddr_in6 *sa =
                                     (struct sockaddr_in6 *) info->ai_addr;
#ifdef IN6_IS_ADDR_V4MAPPED
                        if (IN6_IS_ADDR_V4MAPPED(&sa->sin6_addr)) {
                                const uint8_t *bytes = sa->sin6_addr.s6_addr;
                                struct in_addr addr = { *(const in_addr_t *) (bytes + 12) };

                                memcpy(cxt->hostaddress, &addr, sizeof(struct in_addr));
                        } else
#endif
                                memcpy(cxt->hostaddress, &(sa->sin6_addr), sizeof(sa->sin6_addr));
                }
                freeaddrinfo(info);
        }
}

static void __attribute__((__noreturn__)) usage(void)
{
        fputs(USAGE_HEADER, stdout);
        printf(_(" %s [-p] [-h <host>] [-H] [[-f] <username>]\n"), program_invocation_short_name);
        fputs(USAGE_SEPARATOR, stdout);
        fputs(_("Begin a session on the system.\n"), stdout);

        fputs(USAGE_OPTIONS, stdout);
        puts(_(" -p             do not destroy the environment"));
        puts(_(" -f             skip a second login authentication"));
        puts(_(" -h <host>      hostname to be used for utmp logging"));
        puts(_(" -H             suppress hostname in the login prompt"));
        printf("     --help     %s\n", USAGE_OPTSTR_HELP);
        printf(" -V, --version  %s\n", USAGE_OPTSTR_VERSION);
        printf(USAGE_MAN_TAIL("login(1)"));
        exit(EXIT_SUCCESS);
}

int main(int argc, char **argv)
{
        int c;
        char *childArgv[10];
        char *buff;
        int childArgc = 0;
        int retcode;
        struct sigaction act;
        struct passwd *pwd;
        static const int wanted_fds[] = {
                STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO
        };
        struct login_context cxt = {
                .tty_mode = TTY_MODE,             /* tty chmod() */
                .pid = getpid(),                  /* PID */
#ifdef HAVE_SECURITY_PAM_MISC_H
                .conv = { misc_conv, NULL }       /* Linux-PAM conversation function */
#elif defined(HAVE_SECURITY_OPENPAM_H)
                .conv = { openpam_ttyconv, NULL } /* OpenPAM conversation function */
#endif

        };

        /* the only two longopts to satisfy UL standards */
        enum { HELP_OPTION = CHAR_MAX + 1 };
        static const struct option longopts[] = {
                {"help", no_argument, NULL, HELP_OPTION},
                {"version", no_argument, NULL, 'V'},
                {NULL, 0, NULL, 0}
        };

        timeout = (unsigned int)getlogindefs_num("LOGIN_TIMEOUT", LOGIN_TIMEOUT);

        setlocale(LC_ALL, "");
        bindtextdomain(PACKAGE, LOCALEDIR);
        textdomain(PACKAGE);

        /* TRANSLATORS: The standard value for %u is 60. */
        snprintf(timeout_msg, sizeof(timeout_msg),
            _("%s: timed out after %u seconds"),
            program_invocation_short_name, timeout);

        signal(SIGALRM, timedout);
        (void) sigaction(SIGALRM, NULL, &act);
        act.sa_flags &= ~SA_RESTART;
        sigaction(SIGALRM, &act, NULL);
        alarm(timeout);
        signal(SIGQUIT, SIG_IGN);
        signal(SIGINT, SIG_IGN);

        setpriority(PRIO_PROCESS, 0, 0);
        initproctitle(argc, argv);

        /*
         * -p is used by getty to tell login not to destroy the environment
         * -f is used to skip a second login authentication
         * -h is used by other servers to pass the name of the remote
         *    host to login so that it may be placed in utmp and wtmp
         */
        while ((c = getopt_long(argc, argv, "fHh:pV", longopts, NULL)) != -1)
                switch (c) {
                case 'f':
                        cxt.noauth = 1;
                        break;

                case 'H':
                        cxt.nohost = 1;
                        break;

                case 'h':
                        if (getuid()) {
                                fprintf(stderr,
                                        _("login: -h is for superuser only\n"));
                                exit(EXIT_FAILURE);
                        }
                        init_remote_info(&cxt, optarg);
                        break;

                case 'p':
                        cxt.keep_env = 1;
                        break;

                case 'V':
                        print_version(EXIT_SUCCESS);
                case HELP_OPTION:
                        usage();
                default:
                        errtryhelp(EXIT_FAILURE);
                }
        argc -= optind;
        argv += optind;

        if (*argv) {
                char *p = *argv;

                /* username from command line */
                cxt.cmd_username = xstrdup(p);
                /* used temporary, it'll be replaced by username from PAM or/and cxt->pwd */
                cxt.username = cxt.cmd_username;

                /* Wipe the name - some people mistype their password here. */
                /* (Of course we are too late, but perhaps this helps a little...) */
                while (*p)
                        *p++ = ' ';
        }

        close_all_fds(wanted_fds, ARRAY_SIZE(wanted_fds));

        setpgrp();       /* set pgid to pid this means that setsid() will fail */
        init_tty(&cxt);

        openlog("login", LOG_ODELAY, LOG_AUTHPRIV);

        init_loginpam(&cxt);

        /* login -f, then the user has already been authenticated */
        cxt.noauth = cxt.noauth && getuid() == 0 ? 1 : 0;

        if (!cxt.noauth)
                loginpam_auth(&cxt);

        /*
         * Authentication may be skipped (for example, during krlogin, rlogin,
         * etc...), but it doesn't mean that we can skip other account checks.
         * The account could be disabled or the password has expired (although
         * the kerberos ticket is valid).      -- kzak@redhat.com (22-Feb-2006)
         */
        loginpam_acct(&cxt);

        cxt.pwd = xgetpwnam(cxt.username, &cxt.pwdbuf);
        if (!cxt.pwd) {
                warnx(_("\nSession setup problem, abort."));
                syslog(LOG_ERR, _("Invalid user name \"%s\". Abort."),
                       cxt.username);
                pam_end(cxt.pamh, PAM_SYSTEM_ERR);
                sleepexit(EXIT_FAILURE);
        }

        pwd = cxt.pwd;
        cxt.username = pwd->pw_name;

        /*
         * Initialize the supplementary group list. This should be done before
         * pam_setcred, because PAM modules might add groups during that call.
         *
         * For root we don't call initgroups, instead we call setgroups with
         * group 0. This avoids the need to step through the whole group file,
         * which can cause problems if NIS, NIS+, LDAP or something similar
         * is used and the machine has network problems.
         */
        retcode = pwd->pw_uid ? initgroups(cxt.username, pwd->pw_gid) : /* user */
                                setgroups(0, NULL);                     /* root */
        if (retcode < 0) {
                syslog(LOG_ERR, _("groups initialization failed: %m"));
                warnx(_("\nSession setup problem, abort."));
                pam_end(cxt.pamh, PAM_SYSTEM_ERR);
                sleepexit(EXIT_FAILURE);
        }

        /*
         * Open PAM session (after successful authentication and account check).
         */
        loginpam_session(&cxt);

        /* committed to login -- turn off timeout */
        alarm((unsigned int)0);

        endpwent();

        cxt.quiet = get_hushlogin_status(pwd, 1);

        log_utmp(&cxt);
        log_audit(&cxt, 1);
        log_lastlog(&cxt);

        chown_tty(&cxt);

        if (setgid(pwd->pw_gid) < 0 && pwd->pw_gid) {
                syslog(LOG_ALERT, _("setgid() failed"));
                exit(EXIT_FAILURE);
        }

        if (pwd->pw_shell == NULL || *pwd->pw_shell == '\0')
                pwd->pw_shell = _PATH_BSHELL;

        init_environ(&cxt);             /* init $HOME, $TERM ... */

        setproctitle("login", cxt.username);

        log_syslog(&cxt);

        if (!cxt.quiet) {
                motd();

#ifdef LOGIN_STAT_MAIL
                /*
                 * This turns out to be a bad idea: when the mail spool
                 * is NFS mounted, and the NFS connection hangs, the
                 * login hangs, even root cannot login.
                 * Checking for mail should be done from the shell.
                 */
                {
                        struct stat st;
                        char *mail;

                        mail = getenv("MAIL");
                        if (mail && stat(mail, &st) == 0 && st.st_size != 0) {
                                if (st.st_mtime > st.st_atime)
                                        printf(_("You have new mail.\n"));
                                else
                                        printf(_("You have mail.\n"));
                        }
                }
#endif
        }

        /*
         * Detach the controlling terminal, fork, and create a new session
         * and reinitialize syslog stuff.
         */
        fork_session(&cxt);

        /* discard permissions last so we can't get killed and drop core */
        if (setuid(pwd->pw_uid) < 0 && pwd->pw_uid) {
                syslog(LOG_ALERT, _("setuid() failed"));
                exit(EXIT_FAILURE);
        }

        /* wait until here to change directory! */
        if (chdir(pwd->pw_dir) < 0) {
                warn(_("%s: change directory failed"), pwd->pw_dir);

                if (!getlogindefs_bool("DEFAULT_HOME", 1))
                        exit(0);
                if (chdir("/"))
                        exit(EXIT_FAILURE);
                pwd->pw_dir = "/";
                printf(_("Logging in with home = \"/\".\n"));
        }

        /* if the shell field has a space: treat it like a shell script */
        if (strchr(pwd->pw_shell, ' ')) {
                xasprintf(&buff, "exec %s", pwd->pw_shell);
                childArgv[childArgc++] = "/bin/sh";
                childArgv[childArgc++] = "-sh";
                childArgv[childArgc++] = "-c";
                childArgv[childArgc++] = buff;
        } else {
                char tbuf[PATH_MAX + 2], *p;

                tbuf[0] = '-';
                xstrncpy(tbuf + 1, ((p = strrchr(pwd->pw_shell, '/')) ?
                                    p + 1 : pwd->pw_shell), sizeof(tbuf) - 1);

                childArgv[childArgc++] = pwd->pw_shell;
                childArgv[childArgc++] = xstrdup(tbuf);
        }

        childArgv[childArgc++] = NULL;

        execvp(childArgv[0], childArgv + 1);

        if (!strcmp(childArgv[0], "/bin/sh"))
                warn(_("couldn't exec shell script"));
        else
                warn(_("no shell"));

        exit(EXIT_SUCCESS);
}